Refining mineral oils



Jan. 3, 1939. E. R I EDERER Er AL REFINING MINERAL oILs Filed April 8, 1935 Patented Jan. 3, 1939 UNITED STATES REFINING MINERAL OILS Erwin R. Lederer and George M.

Pfau, Fort Worth, Tex., assignors, by mesne assignments,

to said Lederer Application April 8, 1933, Serial No. 665,088

7 Claims.

This invention relates to a complete process of refining mineral oils and more specically to acid treatment of, and dewaxing of crude oils or fractions or portions thereof.

An object of the present invention is to provide a process for refining crude oils or fractions or portions thereof containing paraiiin wax which process is capable of producing, in particular` lubricating oils of good color and stability, of low cold test and carbon residue and of unusually high viscosity index; and which process is also capable of concurrently producing the lighter fractions, gasoline, kerosene, gas oil, absorption oil, neutral oil, etc., of high quality.

According to the processes now generally in use for the refining of paraffin base or mixed base crudes, the oil is rst subjected to fractional distillation to obtain, if present, the gasoline, naphtha, kerosene, gas oil, and, if desired, other distillates of higher boiling range, and a residual oil, each in separate cuts. Each of these fractions or portions is then separately treated to obtain commarcial products of the required degree of purity. The residual oil and the wax distillate, if such has been separated, are then treated to remove impurities, such as tar, asphalt, etc., and to separate the wax, such treatment involving a long series of steps usually including acid treatment in one or more stages at elevated temperatures, settling after each stage to remove the sludge formed. decolorizing with clay, diluting with naphtha, chilling from a temperature of about 90 1i'. at a rate of a few degrees per hour toa point dependent upon the pour point desired in the lubricating product, separating the precipitated wax by centrifuging, filtering or cold settling, and distilling to remove the diluent added and to obtain the desired lubricating oil as an overhead product or to reduce the residual product to the desired viscosity.

Other objects of the invention are to materially reduce the number of steps heretofore required in refining practice, to reduce the quantity of each refining agent and the quantity and cost of refining equipment and to carry out the process in a continuous manner, thereby to accomplish the refining operation in a more efficient manner than heretofore possible, giving increased yields of products in shorter operating cycles and at a reduced` operating cost.

A still further object of the invention is to treat heavy oils or lubricatingv oils, containing wax or not with sulfuric acid in such manner that the chemical action is entirely under control, such result being obtained by uniformly and thorough- (c1. 19a-1s) 1y treating the oil with the acid for a period of time of controlled duration at very low temperatures of the order of minus 10 F. and below, and immediately centrifuging the treated oil from the acid sludge.

In its broadest aspects the instant invention as applied to a complete refining operation of a low density crude oil comprises chilling the crude oil to a low temperature of from about to plus 30 F., preferably below 10 F., treating with sulphuric or other suitable acid while preventing any excessive increase in temperature, quickly separating the acid sludge formed and the precipitated wax from the treated oil in one and the Same operation as by centrifuging or filtering, decolorizing and neutralizing the oil preferably by a clay treatment and distilling and fractionating the purified oil into the desired fractions and residual oil.

The low density crude oil referred to above denotes a crude having an A.,P. I. gravity in excess of about 35. The instant process is most effective upon oils of an A. P. I. gravity of at least 40 to 43. If the crude or other oil to be treated is t-oo high in density, it is diluted preferably at the outset, with a light petroleum distillate, such as naphtha, or other suitable diluent.

Whereas the above process as described is satisfactory for the rening of most oils, it is necessary in some cases to alter the same or add other steps thereto in order to obtain the best results, as will be hereinafter pointed out. For example, in the treatment of some oils, the separation of the acid sludge at the low temperatures maintained was not thoroughly successful. In an attempt to overcome this objection, it was discovered that the addition to the oil being treated of a small quantity, for example about 0.5 to 5%, of a residue from either a distilling or cracking operation, permits the complete separation of the acid sludge atthe low temperature employed.

In order to facilitate thedescription of the present invention, and to make the nature thereof more readily understandable by others. the accompanying drawing is supplied illustrating diagrammatically one assembly of apparatus in which several variations of the invention may be carried out. It should be understood, however, that such representation is not to be construed as a limitation upon the scope of the present invention as to the number or sequence of steps or to the method of effecting any step or steps.

In the following description of the instant process in connection with the accompanying drawing, the treatment of a parain base crude oil has been selected, the treatment being directed in particular to the production of a high quality lubricating oil of low cold test, as Well as to the production of naphthas, gasoline, kerosene, gas

oils, absorption oils, neutrals, etc.

The process is here described as being totally continuous, but it should be understood that batch treatment can be employed at one or all steps, with a sacrifice of a number of the excellent features and advantages of the invention.

The crude oil to be rened is introduced from a 'source of supply (not shown) through conduit I into pump 2. If the addition of naphtha and/or residual oil are necessary in accordance with the conditions hereinbefore set out, these materials are also introduced, in the predetermined proper quantities, into the conduit I from sources not shown, into pump 2.

The constant stream of oil or oil mixture is forced by the pump through the heat exchanger 3 wherein it is cooled by the cold treated oil passed in indirect contact therewith. The partially cooled oil then passes through the chiller 4 wherein it is cooled to a temperature satisfactorily 10 to 50 F. below the desired pour test of the finished lubricating oil to be obtained which temperature may be anywhere between -70 and plus 30 F. depending upon the product to be produced.

The chiller 4 is of any satisfactory type or construction and may be one in which the oil is cooled by indirect heat exchange with a countercurrent stream of ammonia or chilled brine, the continuous movement of the oil and the removal of any solidified wax deposited on the walls being aided by a screw conveyor rotating therein, whereby the pump 2 is aided in supplying a constant and uniform stream of oil through the apparatus.

From the chiller 4, the cold oil passes to a continuous acid treatment unit or mixer 5, wherein there is mixed with the oil a continuous stream of a constant quantity of sulphuric acid introduced through line 5a. A satisfactory apparatus for obtaining the proper and constant proportioning of acid and oil and for obtaining the necessary intimate admixture thereof is illustrated in application Serial No. 646,230, led December 8, 1932, by one of the present applicants together with others.

'I'he mixer 5 is preferably provided with insulated walls or with refrigerating means to prevent any substantial increase in temperature or the heating of the oil to a point where re-solution of a portion of the precipitated wax will take place, If it is desired to obtain lower temperatures in the mixer the refrigerating means is regulated to effect the same.

In the preferred procedure the cold oil together with the acid sludge formed and the precipitated wax passes from the mixer 5 through the valved conduit 6 to the centrifuge 1 wherein the sludge and wax is quickly separated from the oil in one and the same operation. The wax-acid sludge may be disposed of in any desired manner as by converting it into fuel oil either directly or after recovery of any oil which might be separated by settling.

The treated oil in this single stage embodiment passes through conduits 8, 9 and I0 back to the heat exchanger 3 wherein it cools the incoming oil and becomes heated to about the temperature of the oil charge or to substantially ordinary or atmospheric temperature. From the heat exchanger the oil passes into the clay mixer or treating tank I I into which a constant flow of clay is introduced from a source not shown, through the conduit IIa, any type of automatically operated clay feeder being preferably used. 'Ihe oil is both neutralized and decolorized by this treatment.

The oil-clay mixture is then continuously passed through the conduit I2 to either one of the filter presses I3 wherein the clay and adsorbed impurities are removed. Two presses are provided such that the continuous floW and purification of the oil may be uninterrupted, one press being in use while the other is being dismantled and cleaned.

The purified oil is then ready for distillation and fractionation in any manner desired. In the preferred procedure, the oil from either lter press I3 passes through a heating coil I4 to the fractionating tower I5 wherein the same is flashed and from which any number or kind of fractions may be withdrawn. In usual practice, gasoline or light naphtha is removed from the top at I6, and other fractions, as kerosene, furnace distillate, gas oil, etc., as side streams through lines Il. The several distillates are condensed (condensers not shown) and conducted to storage in the usual manner. In many instances, the distillates are so pure that little or no further treatment is necessary to produce commercial products.

The lubricating oil portion remains in the tower i5 as the condensate in the bottom thereof and is removed through the outlet conduit I8. If a lubricating oil product or products of a viscosity or of viscosities different from that of the oil flowing from the tower I5 is or are desired, the oil is further distilled with or without the aid of steam either at ordinary pressure or at reduced pressure, the product of the desired viscosity being obtained either as a distillate or as a residual portion.

In the treatment of some oils, products of higher Yquality are obtained if the treating process is carried out in two or more stages 1nstead of one, even though the same total amount cf treating agents are employed in both cases. The particular improvement obtained in the lubricating portion is a more thorough removal of the impurities and wax and increase in through-put. In the two stage process, the repeated steps usually include chilling, acid treating and centrifuging of the oil as obtained from the initial centrifuging step. With reference to the drawing, the chilled oil in the mixer 5 is permissibly contacted with a somewhat smaller quantity of acid than employed in the single Astage treatment. After the separation in the in its temperature is again reduced to the low a degree or to an even lower degree than in chiller 4. depending principally upon the desired cold test in the finished lubricating oil to be obtained.

From the chiller I9 the cold oil passes to the mixer 20 wherein it is contacted With an additional quantity of acid from the line 20a, said mixer satisfactorily being of the same construction as mixer 5. 'Ihe treated oil passes to the centrifuge 2| wherein the remaining wax and acid sludge are separated from the oil, the oil passing through conduit 22 into conduit I0 to follow the same course as hereinbefore described.

The second chilling may be omitted where the initial chilling has been to a very low temperature and/or the increase in temperature during the acid treatment and centrifuging has not been too great. In this case the oil from the centrifuge 1 is by-passed around the chiller I9 through conduits 9 and 23 by proper manipulation of valves. The double chilling, however, generally produces the best results. Furthermore, the two stage process in some cases may be altered by omitting the separating step in the centrifuge 1, in which case the oil from mixer 5 passes from the conduit 6 through the by-pass 24 around the centrifuge 1 to be next cooled in chiller I9 and/or acid treated in mixer 20.

In view of the greater elciency of clay and like materials at elevated temperatures, there has been provided as a variation in the present process a heating step adapted to raise the temperature of the oil-clay mixture to a point which will give optimum quality products.` The heating of the oil or oil-clay mixture may be accomplished in any desired suitable manner and is satisfactorily done by the method illustrated on the drawing wherein the oil-clay mixture from the clay mixer Il discharging in conduit l2 is conducted through the heating coil and into the flash tower 26 wherein the naphtha and Water if present may be flashed olf and removed at the top and the oil-clay mixture collecting at the bottom discharged thro-ugh conduit 21 into conduit l2 leading to the filters I3. If necessary to effect efcient operation of the filtration step, the heated oil-clay mixture as obtained from the tower may be first cooled satisfactorily to about 150 F., diluted with naphtha and then filtered.

The clay hereinbefore suggested for use may vbe ordinary clay, activated clay, or revivied clay, in any form, as in water or oil suspension as desired. Instead of clay any other suitable decolorizing agents whether artificial or prepared may be used, including earths, chars, and gels including silica. The decolorizing process may be effected in stages if desired, employing either fresh clay or agent in each case, or used agent followed by fresh agent. If complete neutralization is diflicult by this procedure, the clay treatment may be supplemented by a treatment with soda solution or other such agent preferably effected before the clay treatment. In this manner complete neutralization may be satisfactorily obtained in all cases.

With substantially equal results as far as the quality of the final products is concerned, either or both centrifuges may be replaced by filters or lter presses, the efficient operation of which will usually require the addition of filter aid to the inowing oil, depending upon the nature of the wax precipitated or the ease with which it` may be separated. If filters or presses are employed, continuous filters should be used or a pair should be arranged in parallel to obtain continuous treatment, one being used at a time while the other is being dismantled and cleaned for subsequent use.

Another procedure is available for acquiring some of the advantages to be derived from the instant process. The oil may be treated at any temperature materially below 200 F., and without separating the sludge chilled to a point 10 to 50 F. below the pour point desired in the final product and passed through a separating stage wherein the sludge and precipitated wax are separated from the oil. The oil may then be subjected to the neutralization, decolorization and fractionation steps, preceded or not by a repetition of the treating cycle at low, medium or high temperature. The chilling is preferably effected immediately after the acid treatment and in all cases before the separation of the sludge. A quick chilling and centrifuging prevents excessive secondary i'eactions from taking place in the oil.

The amount of. acid and clay used in the process varies to a considerable extent, depending upon the nature of the oil being treated and the degree of purity desired in the products to be obtained, and must be determined by experiment for each oil to which the process is to be applied. As to the acid the quantity required is from about 25 to 40% less than is necessary to secure the same purity in the ordinary prior processes. The quantity of clay or other similar agent is from 50 to 60% less than in ordinary practice.

Whereas the process of the present invention nas been hereinbefore described in its preferred procedure as a wholly continuous process it shouid be understood that the scope of the invention in its broadest aspects includes batch treatment in any number or all of the steps the use of which obviously sacrifices some of the most advantageous features of the invention.

As has been hereinbefore stated, the present invention is not limited to the treatment of crude oils. Other oils to which it is equally applicable include any fraction or portion of the crude containing paraflin whether it be obtained as an overhead or as a residual oil and whether it is producedby distillation with or without the use of steam and with or without the aid of superatmospheric or subatmospheric pressure, the oils usually having viscosities of from 50 tol 250 seconds at210 F. on the Saybolt Universal viscosimeter. In the appended claims the term mineral oil is used to refer collectively to all of the above materials.

The operation of the instant process in a totally continuous manner to obtain all the benefits derivable by practice of the present invention involves many problems not apparent at first glance. AFor example, the continuous acid treatment can 'be successfully carried out only by the use of accurate metering devices for the a'cid and the oil. The accurate metering of acid is extremely `dif'n'cult due to the corrosive action of the acid upon the metal parts of the metering apparatus employed. A satisfactory apparatus for this purpose is described in application Serial No. 646,230, iiled December 8, 1932.

The thorough and uniform treatment of. the oil with the acid in a continuous manner involves still greater diliculties, which difficulties are overcome in the instant process by the use of a mechanical agitating means composed preferably of several agitator sections and having one or more rotatable disks adapted to cause a shearingaction upon the oil-acid mixture passed between the disks and adjacent surfaces, said oil-acid `mixture being continuously forced through' said agitating means, whereby the oil and acid are uniformly and intimately contacted for a uniform period of time. Such an agitating means isdescribed in the above mentioned copending application. It should be understood, however, that any apparatus giving equivalent results is. satisfactory.

In the continuous separation of the `oil by means of centrifuges it has been found that the rate of flow or through-put can be increased by a slack adjustment of a number of the centrifuges to permit a poor separation of impurities from the oil and by a close adjustment of the remaining centrifuges connected in series to separate and obtain the clean oil. A chilling step or a heating step between the separating operations often leads to a more complete separation of the sludge and/or wax, and such procedure is to be considered within the scope of the present invention.

Many advantages accrue from the practice of the present invention over ordinary prior practice the most outstanding of which are as follows:

1. A shorter operating cycle. The removal of the acid sludge and wax in one and the same operation, eliminates one of the most time consuming operations in present practice. The removal of the acid sludge by centrifuging or filtering instead of by settling saves even more time, the total operating cycle of prior practice being reduced from 5-8 days to 56-70 hours in our process.

2. An increase in viscosity index averaging 3-10 points, in oils treated to date.

3. A lower carbon residue.

4. A reduction in the quantity of acid required, amounting to 25-40%.

5. A reduction in the quantity of clay required to obtain the same color, amounting to 50-60%; or an increase in decolorization using the same quantity of clay.

6. A reduction in the treating losses due to the lower temperature at which the acid treatment is effected, the smaller quantity of acid employed and the more eflicient removal of the sludge.

'7. A great reduction in the quantity and cost of equipment employed. Large expensive treating tanks for agitation and settling are replaced by a small mixer. 'I'he centrifuges heretofore used to separate the wax are replaced by less expensive centrifuges adapted to accomplish the separation of both the wax and the sludge in one operation.

8. A reduction in the heat or fuel required, resulting from the satisfactory neutralization and decoloriza-tion of the oil at ordinary temperatures, rather than at elevated temperatures. The clay treatment is carried out with greater facility, the time and expense of preparing a clay suspension being eliminated.

9. In the treatment of many oils, an elimination of the use of diluents, and in other oils a reduction in the quantity of diluent employed, thus eliminating or reducing the present expense connected therewith, and their recovery costs.

10. An elimination of or a reduction in the amount of treatment necessary to produce finished marketable products from the distillates resulting from the fractionation of the crude oil subsequent to the low temperature acid treatment.

11. A material saving in refrigeration costs and time in effecting the same resulting from the use of direct expansion of ammonia without employing secondary chilling with brine as has been necessary heretofore. Inasmuch as shock chilling is quite satisfactory, the prior slow chilling of ing the oil to a temperature below 0 F., continuously acid treating the chilled oil in a flowing stream, without substantial rise in temperature, and agitating the chilled oil with the acid with the substantial exclusion of air, continuously and quickly centrifuging the acid sludge and wax from the chilled oil without intermediate accumulation of the oil in batches isolated from the stream, continuously neutralizing the acid treated oil and separating the purified oil into the desired fractions.

2. In the refining of mineral oil of an A. P. I. gravity of at least 35 and containing paraffin wax and a heavier lubricating fraction or portion, the steps including chilling the oil to a temperature at which wax precipitates, continuously mixing a stream thereof with sulfuric acid in quantities sufficient to form sludge while preventing substantial increase in temperature and with the substantial exclusion of air, moving the oil-acid mixture to a separator without substantial delay to avoid the formation of undesirable secondary reaction products, and quickly separating the sludge and precipitated Wax simultaneously from the treated oil while still at low temperatures.

3. In the refining of crude mineral oil containing parafiin wax, the steps comprising mixing such oil with a diluent to obtain an A. P. I. gravity of at least 35 and subjecting a stream or streams thereof continuously to treatments comprising chilling to a temperature at which wax precipitates, treating the cold oil with sulfuric acid in quantities sufficient to form sludge, with the substantial exclusion of air, moving the oilacid mixture to a separator without substantial delay to avoid the formation of undesirable secondary reaction products, and quickly separating the sludge and precipitated wax simultaneously from the treated oil while still at low temperatures.

4. The method of simultaneously dewaxing and acid treating mineral oil which comprises diluting the oil to an A. P. I. gravity of at least 35, chilling the oil to a temperature below 0 F., continuously acid treating the chilled oil in a fiovving stream, without substantial rise in temperature, and agitating the chilled oil with the acid, with the substantial exclusion of air, continuously and quickly centrifuging the acid sludge and wax from the chilled oil Without intermediate accumulation of the oil in batches isolated from the stream, repeating the aforesaid acid treating and centrifuging steps at a temperature not materially higher than in the first acid treating step but at least as low as 0 zi F., continuously neutralizing the dewaxed and acid treated oil, and separating the purified oil into the desired fractions.

5. The process as described in claim 4 wherein the oil stream after the initial separation of sludge and wax is chilled to a lower temperature before the second acid treatment.

6. The method of simultaneously dewaxing and acid treating mineral oil containing paraffin wax and a heavier lubricating fraction or portion which comprises diluting the oil to an A. P. I. gravity of at least 35, chilling the oil to a temperature below 0 F., continuously acid treating the chilled oil in a flowing stream without substantial rise in temperature, and agitating the chilled oil with the acid with the substantial exclusion of air, repeating the aforesaid acid treating step at a temperature not materially higher than in the rst acid treating step but at least as lowv as 0 F., and thereafter continuously and quickly centrifuging the acid sludge and wax from the chilled oil Without intermediate accumulation of the oil in batches isolated from the stream.

7. In the refining of mineral oil containing paraffin and a lubricating fraction or portion and having an A. P. I. gravity of at least 35, the combination of steps comprising chilling such oils while possessing acid sludge forming constituents suicient to and of a nature to permit rapidand complete Wax and sludge separation therefrom upon the subsequent treatment herein specified, said chilling being carried to a. temperature from 10 to 40 below the desired pour test, continuously introducing a uniform proportion of acid into the oil-Wax mixture, continuously and uniformly agitating the resulting mixture with the substantial exclusion of air whereby uniform Contact of acid and oil is obtained, and continuously and completely centrfuging the sludge and wax from the purified oil without intermediate accumulation of the oil in batches isolated from the stream.

ERWIN R. LEDERER. GEORGE M. PFAU. 

